1. Field of the Invention
The present invention relates to a dry sump type lubricating system. In particular, the present invention relates to a dry sump type lubricating system capable of reducing the weight and size of an oil tank.
2. Description of Background Art
Dry sump type lubricating systems have been configured such that an oil tank is provided separately from an engine. The oil tank is in communication with a feed pump and a scavenging pump provided on the engine side via oil hoses. For example, Japanese Patent Publication No. Hei 4-3115 discloses a dry sump type lubricating system in which an oil tank is disposed at the back of an engine. The oil tank is supported on a body frame in such a manner as to be separated from the engine. Furthermore, Japanese Utility Model Registration No. 2523715 discloses a dry sump type lubricating system in which an oil tank is supported on a side surface of an air cleaner.
In addition, while not described in the above-described documents, in a dry sump type lubricating system, the pressure in the oil tank is required to be equal to the pressure in the crankcase of the engine. Accordingly, to satisfy such a requirement, for example, as shown by a virtual line in FIG. 3 of the present invention, a pressure-equalization hose 92 may be often formed by connecting a pipe 91 projecting from a top 90 of an oil tank 20 to a crankcase 10 via a pressure-equalization hose 92. In this case, however, to prevent overflowing oil in the oil tank 20 from flowing in the pressure-equalization hose 92, a space capable of containing the overflowed oil must be ensured at an upper portion of the oil tank 20. Accordingly, the size and weight of the oil tank 20 must be increased as shown by the top 90 designated by the virtual line. Furthermore, since the oil tank 20 is connected to the crankcase 10 via the pressure-equalization hose 92, the number of assembling steps increases. Accordingly, an object of the present invention is to solve such a problem.
To solve the above problem, according a first aspect of the present invention, there is provided a lubricating system for an internal combustion engine, including a feed pump for supplying oil in an oil tank to portions to be lubricated of the internal combustion engine, and a scavenging pump for returning oil accumulated in the internal combustion engine to the oil tank, wherein an overflow passage for allowing overflowed oil from the oil tank to flow to the crankcase side is provided between a portion of the oil tank, higher than the oil level, and a crankcase of the engine.
According to a second aspect of the present invention, in addition to the configuration of the first aspect of the present invention, the overflow passage includes a tank side pipe portion integrally formed in the oil tank and a crankcase side pipe portion integrally formed in the crankcase, and the tank side pipe portion is directly connected to the crankcase side pipe portion.
According to the first aspect of the present invention, overflowed oil in the oil tank flows to the crankcase side through the overflow passage provided at a portion of the oil tank higher than an oil level. As a result, a volume for containing the overflowed oil is not required over the oil level of the oil tank. Accordingly, the weight and size of the oil tank can be reduced. Furthermore, since the overflow passage communicates the oil tank to the inside of the crankcase, and thereby functions to equalize the pressure in the oil tank with the pressure in the crankcase, the overflow passage can serve as a pressure-equalization passage as well. As a result, it is not required to provide a pressure-equalization passage separately from the overflow passage.
According to the second aspect of the present invention, since the overflow passage can be formed by directly connecting the tank side pipe portion integrally formed in the oil tank to the crankcase side pipe portion integrally formed in the crankcase, it is not required to connect the oil tank to the crankcase via a separate pressure-equalization hose as in the prior art, with the result that it is possible to reduce the number of assembling steps and hence to facilitate the assembly.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.